<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        #d1, #d2 {
            width: 100px;
            height: 100px;
            border: 1px solid red;
        }

        #d1 {
            /*      margin-top: 50px;
                  margin-left: 50px;
                  margin-bottom: 50px;
                  margin-right: 50px;*/
            /*四个方向*/
            margin: 50px;
            /*上下20,左右50*/
            margin: 20px 50px;
            /*上右下左,顺时针赋值*/
            margin: 10px 20px 30px 40px;
        }

        #d2 {
            /*外边距塌陷
            1.兄弟元素上下相邻,彼此添加外边距取最大值
            2.父子元素上边缘重叠时,添加外边距会取最大值,会导致父子元素粘到一起
            */
            margin-top: 40px;
        }

        #big {
            width: 200px;
            height: 200px;
            background-color: red;
            margin-top: 10px;
            overflow: hidden;
        }

        #big > div {
            width: 50px;
            height: 50px;
            background-color: green;
            margin-left: 50px;
            margin-top: 80px;
        }

        #s1 {
            margin-right: 50px;
        }

        #s2 {
            /*左右相邻彼此添加外边距 不存在外边距塌陷问题,所以是外边距相加*/
            margin-left: 50px;
        }

    </style>
</head>
<body>
<span id="s1">span1</span>
<span id="s2">span2</span>
<div id="big">
    <div></div>
</div>
<div id="d1">div1</div>
<div id="d2">div2</div>
</body>
</html>